The present invention relates to apparatus for rapidly arresting or precluding movement of insulative material in general, and to such apparatus for electrostatically clamping a portion of a continuous web of such material, in particular.
In a coating machine or product assembly machines for assembling insulative (dielectric or semiconductive) material into a finished product, for example, it is often necessary to intermittently arrest the movement of a web of such material, for any number of reasons, for various periods of time. Web motion may be interrupted so that an additional roll of insulative material may be added to the coating machine, a particular assembly operation can be performed on a portion of the moving web at a particular assembly machine workstation, to remedy an unpredictable machine failure or for the performance of routine periodic machine maintenance.
In web coating machines it is extremely important that the tension of web materials being coated in such machines remain fairly constant at all times, including that period of time when web movement is interrupted, in order to avoid changes in web speed during the start-up period when web movement is subsequently re-initiated. Failure to maintain a constant tension level on a web being coated with coating materials flowing at a constant or fixed rate onto a web moving at a varying rate will cause variations in coating thickness that may render the coated web unacceptable for subsequent use in a finished product.
In a product assembly machine for assembling web material into a finished product in which the web has previously had relatively large openings cut therein and these openings are subsequently moved into an assembly machine workstation for the purpose of having an assembly operation performed thereon, web portions adjacent said previously cut openings will often move slightly or develop wrinkles therein because of the web tensioning forces being distributed across a web of reduced cross section. Such novement or wrinkling of the web may cause registration problems or workstation to web misalignment that could substantially reduce the ability of the assembly machine to properly assemble or process the web into a finished product.
In addition to the above, numerous other situations occur where it is either necessary or desirable to be able to rapidly clamp or arrest the motion of insulative materials for various periods of time. Conventional means for handling the above-mentioned problems have been employed with varying degrees of success. Mechanical-type clamping appartus has been ineffective in the control of web tension primarily because of the relatively long times required to apply a clamping force to a lengthy web with such apparatus. It is at least theoretically possible to employ a corona field for insulative web clamping purposes. However, such clamping apparatus would also require extremely long clamping times because of the time required to produce the corona field. The longer the clamping times the greater may be the variation in web tension. Additional disadvantages associated with applying a mechanical clamp to selected portions of a web in a product assembly machine are the relatively large and complex clamping mechanisms that are normally required to properly clamp such selected web portions.
It is a principal object of the present invention to provide apparatus for applying a clamping force to an insulative material within an extremely short period of time.
It is another object of the present invention to provide apparatus that can readily clamp selected portions of an insulative material.
It is a further object of the present invention to provide apparatus for arresting and/or temporarily preventing movement of a continuous web of insulative material.
Other objects as well as features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.